1: πληθύνω
(Strong's #4129 — Verb — plethuno — play-thoo'-no )

used (a) transitively, denotes "to cause to increase, to multiply," 2—Corinthians 9:10; Hebrews 6:14 (twice); in the Passive Voice, "to be multiplied," Matthew 24:12 , RV, "(iniquity) shall be multiplied" (AV, "shall abound"); Acts 6:7; 7:17; 9:31; 12:24; 1—Peter 1:2; 2—Peter 1:2; Jude 1:2; (b) intransitively it denotes "to be multiplying," Acts 6:1 , RV, "was multiplying" (AV, "was multiplied"). See ABUNDANCE , B, No. 5.

2: πλεονάζω
(Strong's #4121 — Verb — pleonazo — pleh-on-ad'-zo )

used intransitively, "to abound," is translated "being multiplied" in the RV of 2—Corinthians 4:15 (AV, "abundant"); the Active Voice, aorist tense, here would be more accurately rendered "having superabounded" or "superabounding" or "multiplying." See ABUNDANCE , B, No. 3.